Collet block

[Raymond AndersonParticipant @raymondanderson34407]

Hello All,

Have purchased 2 square collet blocks er 32, er 40 . I am / was hoping to put one in my 4 jaw independant to use as a collet chuck but have found strange going's on. The chuck face [ Bison Bail ] runs true to less than 0.003mm, but when I set the bore of the collet block to run true [ to within 0.003 mm ] the bar is not held true All collets are cleaned and the bore is also cleaned but no joy. I have checked both blocks using a granite surface plate and a indicator [ Mitotoyo ] that reads to 0.002mm The blocks hold the bar to within 0.01mm so they are good,. this has me stumped. The bar in question is PG steel 16mm dia Any ideas ?

Regards,

Raymond..

[Raymond AndersonParticipant @raymondanderson34407]

[David Clark 13Participant @davidclark13]

Clock the round bar. When true, move the bar round in the collet and clock again. Should still be true.

[JasonBModerator @jasonb]

Collet nut tight enough? what quality collets? Chuck jaw faces could be tilting the block slightly away from chuck face

Edited By JasonB on 06/09/2015 10:08:33

[colin hawesParticipant @colinhawes85982]

Try feeler gauge between collet block base and chuck face. I would put two strips of paper in parallel there and tap the block into place against them with a soft mallet. Both paper strips should be held tight to prove the block is seating properly. If not you may have surface damage on the chuck face or the block end face isn't square to its bore.Minor roughness or burrs on the chuck face or block is best removed using a flat oilstone. Colin

[Raymond AndersonParticipant @raymondanderson34407]

Hello David / Jason Just in from trying various tests, Set the bar true at 75mm from the collet nut face move to 25mm from the collet nut face and 0.11 run out, moved back to 75mm from face rotated collet 90 deg still true to within 0.02mm

Checked the bar with v blocks and granite surface plate and it is straight to within 0.01mm Bar length 150mm.

Next test is to check the chuck jaws by gripping the same bar and see what the results are.

The collets are standard ones, but even with my Rohm ones the readings are not much better..

[Raymond AndersonParticipant @raymondanderson34407]

Hi Colin just noticed your reply, The collets block is tapped hard against the chuck face. In case the end is not perfectly square to the bore, then I will also try keeping the rear face away from the chuck face slightly. and see what I get.

[Nigel McBurney 1Participant @nigelmcburney1]

Have you checked the roundness of the test bar,centre less ground bar can be ground to a lobe shape,check with a micrometer and it shows a constant diameter ,place the bar in a vee block set, up a dial gauge and then rotate the bar, if it is lobed the dial gauge will indicate the error,if it is ground true the dial gauge should be constant. It is caused by the centreless grinder not being set up correctly. You show clock readings to three decimal places ,have you read the gauge correctly,if so then you are expecting an awful lot of quality from a collet block. I have a hex er32 collet block ,have found it the ideal method to make whit thread studs for stationary engines,the er collets have fantastic grip and allow short studs with only half an inch of central plain steel (EN8) to be threaded each end without the bar slipping ,The block is held in the three jaw and the die in a sliding die holder, the er collet nut also allows the die to go right up to the collet face, I would not use my lathe collets in this way as I was taught that ordinary spring collets (5c and similar)should only be tightened just sufficiently to hold the work for turning. The ers can be really pulled tight and it does not matter if one does get damaged they are quite cheap, The collet block can also be held in the bench vice to grip round rod when it needs to be threaded using a die holder,far better than vice jaws and no marking.Never checked the accuracy of the block as I only use it for studs where concentricity dos not matter.Its solved the grip problem and has made stud making easy and quick,previously it was a pain in the backside,best tool I have bought for ages.

[Raymond AndersonParticipant @raymondanderson34407]

Hi Nigel,

Yes, I did read the indicator correctly. I dont expect fantastic readings from the blocks but would have expected better than 0.11 The collet blocks are not at fault and the bar is true when rorated in the v blocks so the bar is not the problem Did a test on the chuck jaws gripping the bar and it would appear to be them at fault as 75mm from the chuck jaws I set the bar true and moving toward the chuck by 50mm results in an eccentric reading. Will keep the collet blocks as they are great, and I will purchase a Collet chuck for the lathe.

I was hoping this way would save me having to change over the 4 jaw, but best if I get a proper ER lathe chuck.

and mount it on a D1-5 Camlok backplate.

Regards.

[BazyleParticipant @bazyle]

There have often been articles in ME about truing 3 jaw chuck jaws. Normally for concentricity but a side effect is parallelism. Same techniques should apply to 4 jaw.

[Enough!Participant @enough]

Raymond, there's an article in the current (Sept 2015 Issue 232) about improving the accuracy of ER collets. The author apparently found that the initial tightening didn't produce the best accuracy and that it could be improved by tapping the collet nut.

Haven't tried it myself but it might be worth a read in relation to your problem.

[ One thing I thought was missing from the article – and perhaps relevant – was where the workpiece fit within the clamping range of the collet ].

[Raymond AndersonParticipant @raymondanderson34407]

Hi All, I put some micrometer blue on each of the 4 jaws and it would appear to grip the bar along the full length of all the jaws. before the blue, I thought that they were off a little, but that appears not to be the case.

I have ordered up a ER40 lathe chuck so,I wont bother doing any more tests.

Regards.

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